The invention relates to a valve timing control device for an internal combustion engine which variably controls valve-open and valve-closure timings of intake-port side and exhaust-port side engine valves, depending upon engine operating conditions.
A conventional valve timing control device has been disclosed in Japanese Patent Provisional Publication No. 10-153104.
Briefly speaking, in this conventional valve timing control device, a timing pulley (a driving rotational member), driven by a crankshaft of an engine, is coaxially installed on the outer periphery of a shaft member (a driven rotational member) integrally connected to a camshaft, and the timing pulley and the shaft member are coupled with each other via an installation-angle adjusting mechanism. The installation-angle adjusting mechanism is constructed mainly by a piston member (a movable operating member) that the relative rotation of the piston member to the timing pulley is restricted but the axial displacement of the piston member is permitted, and helical gears formed the inner peripheral wall surface of the piston member and the outer peripheral wall surface of the shaft member and being in meshed-engagement with each other. The installation-angle adjusting mechanism serves to adjust the installation angle between the timing pulley and the shaft member via the helical gears by moving the piston member in either one of axial directions by way of a control mechanism including electromagnets and a return spring.
The previously-noted conventional valve timing control device has the difficulty in holding the rotational phase against reaction force (alternating torque) caused by the engine valves. For this reason, in addition to the piston member, an electromagnetic clutch, used to hold the phase, is further provided.
It is, therefore, in view of the previously-described disadvantages of the prior art, an object of the present invention to provide a valve timing control device for an internal combustion engine which is capable of enhancing ease of assembly or mounting on the vehicle, while reducing the axial installation space occupied by the installation-angle adjusting mechanism.
It is another object of the present invention to provide a valve timing control device for an internal combustion engine which is capable of certainly holding a rotational phase against reaction force created by engine valves without providing a more complicated structure and using electromagnetic parts.
In order to accomplish the aforementioned and other objects, a valve timing control device of the invention comprises a driving rotational member driven by a crankshaft of an engine, an engine valve provided at an associated one of an intake port and an exhaust port for opening and closing the associated port, a valve spring biasing the engine valve in a direction closing of the associated port of the intake and exhaust ports, a driven rotational member including either one of a camshaft having a cam that opens the engine valve against a spring bias of the valve spring and a separate member integrally connected to and separable from the camshaft, and an installation-angle adjusting mechanism disposed between the driving and driven rotational members to transmit a torque of the driving rotational member to the driven rotational member and having a movable operating member that varies a relative-rotation phase between the crankshaft and the camshaft by way of movement of the movable operating member in a radial direction of the camshaft depending on engine operating conditions.
The other objects and features of this invention will become understood from the following description with reference to the accompanying drawings.